Preheat a cast-iron skillet over medium heat. Toss the chicken thighs with the oil. Starting with the skin side down, cook the thighs until the skin is very crisp. Turn and cook them until done. Sprinkle the crisp skin with a little salt. (The chicken may also be roasted, skin side up and uncovered in a 375 degree oven until well-done and golden-crisp.)

While chicken is cooking, mix up the crema. Stir together sour cream, ancho and lime juice. Allow to sit so that flavors meld. 

When the chicken is cooked, slice it thinly or dice it. Place it in a bowl and toss it with the garlic and serrano chile, 1 teaspoon of salt and a couple grinds of fresh pepper. Squeeze the lime juice and lemon juice directly over the chicken, add the mezcal, and stir in the cilantro.

Place spoonfuls of chicken in the warm tortillas, top with shredded lettuce, avocado and crema.